Agent Skills: sync-skill-taxonomy

Classify every skill in skills/ as user-invoked or model-invoked, ensure disable-model-invocation is set on user-invoked skills, and inject metadata.category on all. Run after adding or changing skills, or when token-cost/routing quality is being reviewed. Use for \"sync skill taxonomy\", \"classify skills\", \"fix disable-model-invocation\", or \"skill token audit\".